AQA A Level Biology

Revision Notes

8.2.1 Totipotent Cells

Totipotent Cells

  • A stem cell is a cell that can divide (by mitosis) an unlimited number of times
  • Each new cell that is produced when a stem cell divides has the potential to remain a stem cell or to develop into a specialised cell such as a blood cell or a muscle cell (by a process known as differentiation)
  • This ability of stem cells to differentiate into more specialised cell types is known as potency
  • There are three types of potency:
    • Totipotency
    • Pluripotency
    • Multipotency

Totipotent Cells

  • Totipotent cells can divide and produce any type of body cell
  • This type of stem cell is also referred to as ’embryonic stem cells
  • Totipotent cells exist for a limited time in early mammalian embryos, as well as in extra-embryonic cells (the cells that make up the placenta)
  • The zygote formed when a sperm cell fertilises an egg cell is totipotent, as are the embryonic cells up to the 16-cell stage (morula) of human embryo development
  • Initially, the totipotent cells in the embryo are unspecialised
  • During development, totipotent cells begin to translate only part of their DNA, which results in cell specialisation
  • These specialised cells then form tissues and are no longer classed as totipotent
  • There are no totipotent cells present in the later stages of development as cells lose their ability to differentiate into any cell type

Exam Tip

It is useful to remember totipotent cells as being able to produce the total amount of possible cells found in the body.

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